Mechanism to update the CSG cell access check upon PLMN change at handover

ABSTRACT

Solving dual errors for user equipment UE checking whether a private cell is allowed when handing over between serving and target cells, where the PLMN and/or EPLMNs list of the serving and target cells may differ. The serving cell may send a one-bit indication that there is a change in a handover command or system information SI6 message after which the UE may or may not refrain from reporting new cells until it performs a registration/location area update in the target cell. The target cell may trigger in the UE a registration update then provide the UE with the PLMN of the target cell. The serving cell can provide the PLMN of the target cell in a SI6 message or handover command, which the UE may use in place of or in addition to the PLMN/EPLMN of the serving cell when checking whether a private/closed subscriber group cell is allowed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a Continuation of U.S. patent application Ser. No. 13/214,528,filed Aug. 22, 2011, and claims the benefit under 35 U.S.C. 119 of GB1114430.0, filed Aug. 22, 2011, the entire disclosure of each of whichis incorporated herein by reference.

TECHNICAL FIELD

The exemplary and non-limiting embodiments of this invention relategenerally to wireless communication systems, methods, devices andcomputer programs, and more specifically relate to updating andmaintaining corrects lists at a user equipment for closed subscribergroup cells.

BACKGROUND

The following abbreviations used in the specification and/or thedrawings are defined as follows:

3GPP third generation partnership project

BSS base station system

CSG closed subscriber group

DL downlink (network towards UE)

eNodeB base station of a LTE/LTE-A system

EPLMN equivalent PLMN

E-UTRAN evolved UTRAN

GERAN GSM/edge radio access network

GSM global system for mobile communications

ID identifier

LAU location area update

LTE long term evolution (of the UTRAN system)

MME mobility management entity

MSC mobile switching center

NAS network access stratum

PLMN public land mobile network

S-GW serving gateway

RAT radio access technology

RR radio resource

UE user equipment

UL uplink (UE towards network)

UMTS universal mobile telecommunication system

UTRAN universal terrestrial radio access network

In the E-UTRAN system relevant to these teachings there are conventionalnetwork access nodes/cells termed eNodeBs which serve all users, andalso subscriber group CSG cells such as home eNodeBs which are availablefor traffic (voice and/or data) to only those subscribers registeredwith the CSG and possibly also certain allowed guests. Any given CSG mayinclude a group of cells (such as a corporate or university campus) or asingle cell. CSGs may allow traffic access for non-subscribers foremergency calls but these teachings relate to routine, non-emergencyaccess.

These different types of cells or access nodes may be termed moregenerally as public access nodes/public cells and private accessnodes/private cells. Other wireless systems (GERAN, GSM, UTRAN, WCDMA)have either implemented or are considering implementing similar suchprivate cells as more functionality is shifted from higher in the radioaccess network toward the base stations/access nodes. In these systemsthe UE is to keep a list, termed a CSG whitelist or CSG allowed list,which recites all the identities of the CSG cells for which thatparticular UE has access rights. Other radio access technologies RATsuse similar whitelists which may be known by different terms. For LTEand UMTS the CSG whitelist is a combination of the UE's allowed CSG listand the operator's CSG list (see for example 3GPP TS 2342.2 v10.4.0 forfurther details).

Many mobile user radios are now capable of operating in multiple RATs,and the examples below are in the non-limiting context of a HE handingover between GERAN cells and checking if a nearby UTRAN/LTE CSG cell isallowed. In recent 3GPP discussions related to the handling of the CSGwhitelists when the UE performs its access check (where the UE checks ifa given CSG is allowed or not) prior to reporting of the CSG cellresulted in agreement that the UE should take into account the list of“equivalent PLMNs” in addition to the registered and selected PLMN (seefor example document SP-110415 entitled LS ON EQUIVALENT PLMN [TSG SAMeeting #51; Bratislava, Slovakia; 6-8 Jun. 2011]. The CSG whitelistcontains [CSG ID, PLMN ID] pairs indicating which CSGs in which PLMNsthe mobile station is allowed to access. Hence a CSG cell is allowed fora UE if, in addition to the cell's CSG ID being in the whitelist, itsassociated PLMN ID is determined as a valid one by the UE, valid beingequal to the PLMN ID of the selected PLMN or the registered PLMN or oneof the PLMNs in its EPLMN list. In dedicated mode, the registered andselected PLMNs are the same.

3GPP TS 24.008 v10.3.0 (2011-06) provides that the UP, will locallystore a list of EPLMNs received from the network in which it isregistered. This list is replaced or deleted at the end of eachlocation/registration update procedure, routing area update procedureand CPRS attach procedure. The stored list consists of a list ofequivalent PLMNs as downloaded by the network plus the PLMN code of theregistered PLMN that downloaded the list. A problem arises in that whenhanding over between cells, the UE will not always have the correctPLMN/EPLMN and so its view of what nearby CSG cells are allowed is notalways accurate.

FIG. 1 illustrates a relevant wireless environment: a UE 20 is undercontrol of a GERAN cell-A 24 which is in PLMN1 and is handing over toanother GERAN cell-B 28 in PLMN2.Nearby there is a CSG cell-C 30 withPLMN-IDa. Cell-A 24 is the UE's serving cell and so the UE obtains fromcell-A 24 its (first) whitelist 101, which the cell-A 24 gets from itsMSC-A 22 and which includes PLMN1 and list EPLMN1. Along with the CSGIDs, this is the whitelist the UE 20 has stored in its memory. The validPLMNs for the UE 20 in cell-B 28 are in its (second) whitelist, whichcell-B 28 obtains from its MSC-B 26 and which includes PLMN2 and EPLMN2.For this UE 20, CSG cell-C 30 with PLMN-IDa may not be an allowed cellin cell-A 24 (if PLMN-IDa is not within the set {PLMN1, EPLMN1}) but itcould be an allowed in cell-B 28 (if PLMN-IDa is within the set {PLMN2,EPLMN2}) or vice versa. CSG cell-C 30 is a potential target cell forhandover and ideally the mobile station 20 should determine prior toreporting the CSG cell-C whether it is an allowed cell.

In the GERAN dedicated mode upon handover to a cell of a differentlocation area, the location area update (AU) procedure can only beperformed after the dedicated connection is released. While a LAU mayonly be triggered by the UE, unlike the network the UE is notnecessarily aware of the change of location area at handover. Thus it isnot aware that there may be a change to the PLMN or EPLMN lists. Thishad not been an issue previously because only recently has mobility toCSG cells been considered.

Mobility to CSG cells in the connected/dedicated mode relies on theability of the UE to report CSG cells and on the ability of the networkto hand the UE over to a previously reported CSG cell. If a UE 20 in theconnected/dedicated mode needs to report a UTRAN CSG cell-C 30 as inFIG. 1 which is in cell-B 28, then the CSG access check performed by theUE 20 for the CSG cell-C 30 identified as (CSG-IDa, IDa) may not yieldthe correct allowed/not allowed decision because the UE 20 does notnecessarily have the correct whitelist set {PLMN2, EPLMN2} that isassociated with that cell-B 28.

One approach to resolve this issue is noted at document S2-112640,entitled INTERPLMN HANDOVER TO A CSG CELL by Samsung, Nokia SiemensNetworks and Huawei [3GPP TSG SA WG2 Meeting #85; Xian, China; 16-20 May2011]. This document is a change request for 3GPP TS 23.401, andspecifically it sets forth that the source network validate the CSGmembership of the UE in the target CSG cell using the CSG-ID list of theserving PLMN-ID before allowing the handover. As will be detailed below,this is seen to be only a partial solution for it fails to address theproblem in which, due to the UE 20 not having the valid list of EPLMNs,the nearby CSG cell is not even reported by the UE when in fact thatnearby cell is an allowed CSG cell.

Embodiments of these teachings detailed below resolve the above problemsin correctly identifying handover CSG cells across different PLMNs.

SUMMARY

In a first exemplary embodiment of the invention there is an apparatuscomprising at least one processor and at least one memory storing acomputer program. In this embodiment the at least one memory with thecomputer program is configured with the at least one processor to causethe apparatus to at least: detect that for a user equipment there is achange to at least one of a PLMN and a list of equivalent PLMNs betweena serving cell and a target cell, and thereafter send to the userequipment an indication of the detected change during a handover of theuser equipment in dedicated or connected mode from the serving cell tothe target cell.

In a second exemplary embodiment of the invention there is a methodcomprising: detecting that for a user equipment there is a change to atleast one of a PLMN and a list of equivalent PLMNs between a servingcell and a target cell, and thereafter sending to the user equipment anindication of the detected change during a handover of the userequipment in dedicated or connected mode from the serving cell to thetarget cell.

In a third exemplary embodiment of the invention there is a computerreadable memory storing a computer program, in which the computerprogram comprises: code for detecting that for a user equipment there isa change to at least one of a PLMN and a list of equivalent PLMNsbetween a serving cell and a target cell, and code for sending to theuser equipment an indication of the detected change during a handover ofthe user equipment in dedicated or connected mode from the serving cellto the target cell.

In a fourth exemplary embodiment of the invention there is an apparatusfor use in a user equipment for maintaining closed subscriber groupcells, the apparatus comprising at least one processor and at least onememory storing a computer program. In this embodiment the at least onememory with the computer program is configured with the at least oneprocessor to cause the apparatus to at least: during a handover of auser equipment in a dedicated or connected mode from a serving cell to atarget cell, receive signaling indicating that there is a change to atleast one of a public land mobile network PLMN and a list of equivalentPLMNs between a serving cell and a target cell, and utilize at least oneupdated PLMN to check whether a private cell is allowed for the userequipment.

In a fifth exemplary embodiment of the invention there is a method foruse in maintaining closed subscriber group cells in a user equipment,the method comprising: during a handover of the user equipment in adedicated or connected mode from a serving cell to a target cell, theuser equipment receiving signaling indicating that there is a change toat least one of a public land mobile network PLMN and a list ofequivalent PLMNs between a serving cell and a target cell, and the userequipment utilizing at least one updated PLMN to check whether a privatecell is allowed for the user equipment.

In a sixth exemplary embodiment of the invention there is a computerreadable memory storing a computer program, in which the computerprogram comprises: code for, during a handover of a user equipment in adedicated or connected mode from a serving cell to a target cell,receiving signaling indicating that there is a change to at least one ofa public land mobile network PLMN and a list of equivalent PLMNs betweena serving cell and a target cell, and code for utilizing at least oneupdated PLMN to check whether a private cell is allowed for the userequipment.

These and other embodiments and aspects are detailed below withparticularity.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic diagram illustrating an environment in whichembodiments of the invention may be practiced to advantage.

FIG. 2 is a signaling diagram illustrating signaling and actions takenin accordance with a first exemplary embodiment of the invention.

FIG. 3A is a new type 1 information element entitled“PLMN/EPLMNList_CHANGE Indication” for implementing these teachings inaccordance with an exemplary embodiment.

FIG. 3B is a table defining the information element of FIG. 3A inaccordance with an exemplary embodiment.

FIGS. 4A-B are logic flow diagrams that each illustrates the operationof a method, and a result of execution of computer program instructionsembodied on a computer readable memory, in accordance with the exemplaryembodiments of this invention.

FIG. 5 is a simplified block diagram of various network devices and a UEsimilar to those shown at FIG. 1, which are exemplary electronic devicessuitable for use in practicing the exemplary embodiments of theinvention.

DETAILED DESCRIPTION

The UE 20 may be served by a different location area in a different PLMNthan the one in which it last made a registration update such that thisPLMN and/or the associated list of EPLMNs may be different from the UE'sregistered PLMN and EPLMN list obtained at the last registration update,e.g. across country borders. This is the FIG. 1 scenario. The networkside may be aware of the different location areas but the UE upon ahandover from serving cell-A 24 to target cell-B 28 will not know thatthere is a change of location area. And so the conventional access checkon CSG 30 performed by the UE 20 utilizing potentially obsolete PLMN andEPLMN lists can yield the following two distinct errors. The first istermed a false match, in which a CSG cell 30 that the UE 20 determinesas allowed (and hence possibly reported as a handover candidate) may notbe an allowed CSG cell for that UE 20. The second is termed a missedmatch, in which an allowed CSG cell 30 may not be determined by the UE20 as allowed (and hence not reported by the UE 20 at all).

These are detailed with respect to the example at FIG. 1. The UE 20 isin a cell 24 under PLMN1 and has EPLMN List 1 where PLMN1 is theregistered PLMN (rPLMN=PLMN1) of the UE 20. The UE 20 is handed over toa new cell 28 which is in PLMN2 (with EPLMN List 2). As the mobilestation 20 is in dedicated mode no LAU takes place in the UE 20 whichstill assumes that rPLMN=PLMN1, and still uses the EPLMN List 1 sincethe UE is still using its previously stored {PLMN1, EPLMN1} after thehandover to the new cell 28. The UE 20 does not know that in the newcell 28 PLMN2 and EPLMN List 2 apply. The UE 20 then identifies the CSGcell-C 30 as having CSG IDa and PLMN IDa and performs an access checkusing its stored whitelist which has {PLMN1, EPLMN1}.

In a first example this access check shows CSG cell-C 30 is an allowedCSG cell because CSG IDa and PLMN IDa are in the UE's stored CSGwhitelist which has {PLMN1, EPLMN1}. The false match error occurs ifPLMN-IDa is equal to one PLMN of {PLMN1; EPLMN1} resulting in a matchbut where in fact the PLMN IDa is not equal to one of the correct MANIDs {PLMN2, EPLMN2}. The UE 20 has erroneously determined that the CSGcell-C 30 is allowed for it and the UE 20 may incorrectly report CSGcell-C 30. The access check should not have passed but did, leading tothe UE 20 reporting to the new cell 28 the CSG cell-C 30 parameterswhich represents a large GERAN signaling load, all wasted effort in thiscase.

In a second example this access check shows CSG cell-C 30 is not anallowed CSG cell because while CSG-IDa and PLMN-IDa are in the correct(second) CSG Whitelist, PLMN-IDa is not equal to one of {PLMN1; EPLMN1}which the UE 20 incorrectly still considers valid. The missed matcherror occurs because the PLMN-IDa is equal to one of the correct PLMNIDs {PLMN2, EPLMN2} but the UE 20 finds no match for it in its currentlist {PLMN1, EPLMN1}. The UE 20 has erroneously determined that the CSGcell-C 30 is not allowed (or equivalently has not determined it asallowed) and so the UE 20 will not report it to the new cell 28. Theaccess check should have passed but did not, leading to the UE 20 nothanding over to the allowed CSG cell-C 30 despite that it might be thebest handover candidate. It is this missed match which the documentS2-112640, referenced in the background section above, does not appearto address.

Note that in this second example network sharing may apply. Networksharing occurs when a cell is shared by more than one PLMN. For networksharing the different PLMNs sharing this CSG cell-C 30 need to be takeninto account, if broadcast in this new cell 28, in the above examples itis assumed that PLMN2 and the list of PLMNs PLMN and other PLMNs)sharing this cell can be used interchangeably.

The exemplary embodiments presented herein resolve both the above errorsby providing for a detection whether the UE's registered PLMN and EPLMNlist which were used in the old cell 24 are made invalid by the PLMN andassociated EPLMN list in the new cell 28. This detection may be done bythe UE (after handover from old serving cell 24 to target/new servingcell 28), or by the network (prior to handover from old serving cell 24to target/new serving cell 28), or by both. In one variation, based onthe detection a registration update of the UE in dedicated mode is madeafter successful completion of the handover to the new cell 28, in orderto update the UE 20 with its new registered PLMN and EPLMN list. Inanother variation, based on the detection the network 28 performs theaccess check with the correct {PLMN, EPLMN list} for this UE 20 in thenew cell 28 for each CSG cell that the UE 20 reports in the new cell 28in dedicated/connected mode to correctly determine whether the reportedCSG cell 30 is allowed or not, at least as long as no registrationupdate is made for or by the UE in the new cell 28.

While the above procedure is seen to be most advantageous in thecircuit-switched domain, it can also be used in the packet-switcheddomain when the registered/serving PLMN and EPLMN list is expected tochange but where no update to location area, routing area or trackingarea is to be performed after the handover from cell 24 to cell 28.

Further are described various embodiments for implementing the abovedetection of whether the UE's registered PLMN and EPLMN list from theold cell 24 are invalid in the new cell 28. Each of these is noted asresolving the false match or the missed match errors to one extent oranother. Afterwards are detailed various suggested combinations of thedifferent embodiments which provide a more complete solution to the dualerrors noted above by example. Combinations other than those suggestedmay of course be implemented without departing from the scope of theseteachings.

Whether the old PLMN and EPLMN list are invalid for the new cell 28 maybe detected by comparing the PLMN sets. Stated more concisely, thisdetection tests for at least one of the following intersections of sets:{rPLMN,EPLMN list} _(old cell) ∩{PLMN,EPLMN list} _(new cell)=Ø; or{rPLMN,EPLMN list} _(old cell) ∩{PLMN} _(new cell)=Ø; or{rPLMN} _(old cell) ∩{PLMN,EPLMN list} _(new cell)=Ø;where rPLMN is the registered PLMN of the old cell (cell 24 in FIG. 1).As noted above, if the detection is done by the network (e.g., by cell-B28 and/or MCS-B 26 in FIG. 1) it is done during preparation for handingover the UE/mobile station 20 to a private cell (CSG cell-C 30 in FIG.1), and if done by the UE/mobile station 20 it may be done duringexecution of the handover from cell 24 to cell 28 itself or after thesuccessful completion of that handover.

In a first embodiment for the network side implementation of the PLMNvalidity detection, the UE does not report CSG cells until/unless thereis a registration update procedure. In this first embodiment the highernetwork node MSC-B 26 and subsequently the old cell 24 indicates theresult of the detection in the handover signaling, and that theUE/mobile station 20 is notified of this detection at handover (forexample, in the RR HANDOVER COMMAND message from the old cell 24). Thisnotification is used to order the UE/mobile station 20 to not report anyCSG cells 30 while in the dedicated mode after successful completion ofthe handover to the new cell 28, at least as long as no successfulregistration update is made in the LIE/mobile station 20 in the new cell28. This first embodiment resolves the false match problem detailed byexample above. The notification is in one implementation provided via anewly introduced indicator in the handover signaling, termed herein aPLMN/EPLMNList Change Indicator. In this case the PLMN/EPLMNList ChangeIndicator is set by the network. Examples of such a PLMN/EPLMNListChange Indicator are detailed below with respect to FIGS. 3A-B.

In a second embodiment the UE/mobile station 20 continues to report tothe network/new cell 28 any CSG cells 30 which pass the UE's accesscheck with the {PLMN,EPLMN list}_(old cell) until there is aregistration update, irrespective of the {PLMN, EPLMN list} change. Thisembodiment also has the network itself do the PLAIN validity detectionsimilar in concept to that described in S2-112640 (see above), but inthis case the network/new cell 28 performs the access check with thecorrect {PLMN, EPLMN list}_(new cell) in the new cell 28 for each CSGcell reported by the UE/mobile station 20 in the new cell while theUE/mobile station 20 is in the dedicated mode after successfulcompletion of the handover. The network/new cell 28 continues performingthis check at least until there is a successful registration update madein the UE/mobile station 20 in the new cell 28. This registration updategives the UE/mobile station 20 the correct {PLMN, EPLMN list}_(new cell)which enables the UE 20 to accurately determine whether any CSG cell isallowed or not. This second embodiment also resolves the false matchproblem detailed by example above, but not completely.

Conventionally it is the UE/mobile station 20 which initiatesregistration or location area updates. In a third embodiment also inwhich the PLMN validity detection is implemented by the network/new cell28, the network triggers an unsolicited registration update (notrequested by the UE) in the UE/mobile station 20 while that UE/mobilestation 20 is in the dedicated mode. Since currently there is nomechanism for the network to initiate a registration update, in oneimplementation for this third embodiment the UE/mobile station 20 firstindicates to the network/new cell 28 that it supports receiving anunsolicited registration update message while in the dedicated mode.This triggering occurs after successful completion of the handover tothe new cell 28. In one aspect this third embodiment is implemented bythe formerly serving network (old cell-A, 24) sending a NAS or RRmessage, which includes the PLMN ID of the PLMN which is now serving theHE/mobile station 20 in the new cell 28 as well as the associated EPLMNlist, for use by the UE/mobile station 20 in the new cell 28 so theUE/mobile station 20 can update its registered PLMN and EPLMN listaccordingly. The EPLMN list is normally conveyed by the NAS, so it is asimpler implementation that NAS signaling be used for sending the newcell 28 the set {PLMA, EPLMN}_(new cell) as well. By example the set{PLMN, EPLMN}_(new cell) may be sent in a LOCATION UPDATING ACCEPTmessage from the old cell 24 to the UE/mobile station 20. This thirdembodiment addresses the missed match problem noted by example above.The various suggested combinations of embodiments noted below addresshow to handle the CSG cells before the registration update is made inthe new cell 28.

In a fourth embodiment the network may provide to the UE/mobile station20 (which is in the dedicated mode) a system information message whichcontains the location area identifier of the new cell 28 (for example, aSYSTEM INFORMATION TYPE 6 SI6 message). The location area identifierincludes the PLMN ID of the new cell 28 along with the location areacode. This is possible in conventional GERAN but restricted to the useof voice group call service VGCS and voice broadcast service VBS. Thisfourth embodiment expands the use of the location area identifier in thesystem information type 6 message when both the old cell 24 and theUE/mobile station 20 support interworking with CSG cells 30 while theUE/mobile station 20 is in the dedicated mode. Note that the network/oldcell 24 in this case would not necessarily make a PLMN validitydetection before sending the SI6 message. The UE/mobile station 20 inthe dedicated mode can use the PLMN ID it received in the SI6 to detectthat {rPLMN, EPLMN list}_(old cell)∩{PLMN}_(new cell)=Ø, and thus theUE/mobile station 20 would detect the PLMN validity itself.

For the case of network sharing where a cell is shared by more than onePLMN, the above assumes that PLMN_(new cell) andMultiplePLMNs_(new cell) can be used interchangeably, where the termMultiplePLMNs_(new cell) is the list of PLMNs sharing the new cell 28.In case of network sharing, the network 24 should indicate in the systeminformation type 6 message the PLMN ID of the PLMN on which theLIE/mobile station 20 is registered (as per the handover) even if theUE/mobile station 20 is yet to know it is registered in this (new) PLMN.It is not necessary that the Old cell 24 needs to indicate the list ofPLMNs sharing the new cell 28, but in case it does the UE/mobile station20 should not take into account any PLMN in this list that would be partof the list of forbidden PLMNs (unless of course the UE/mobile station20 is attached to the new/restricted cell 30 for emergency services).

In this fourth embodiment, the PLMN validity detection by the UE/mobilestation 20 can be triggered by a PLMN validity detection by the old cell24 and the associated signaling from the old cell 24 at the handover,such as the above-mentioned RR HANDOVER COMMAND message. Thereafter,based on the UE/mobile station's PLMN validity detection the UE/mobilestation 20 in the dedicated mode can request a registration update fromthe new cell 28 through NAS signaling, such as the above-mentionedLOCATION UPDATING REQUEST message. This will trigger in the new cell 28a conventional (solicited) registration update by NAS, for example aLOCATION UPDATING ACCEPT message which the new cell 28 sends to theUE/mobile station 20 to indicate the PLMN and EPLMN list in the new cell28. From this the UE/mobile station 20 can update its memory with thenew registered PLMN and EPLMN list {PLMN2, EPLMN2} accordingly.

The fourth embodiment addresses the missed match problem only, and so acomplete solution (noted below) needs to also address the false matchproblem. Additionally, one aspect for implementing this fourthembodiment is for the old cell 24 to signal to the UE/mobile station 20that it is allowed to send, while in the dedicated mode, a request forregistration update. In the 3^(rd) embodiment the new cell 28 sends anLAU Accept message without receiving the LAU Request message from themobile station 20 and only after the successful handover, while in the4^(th) embodiment the mobile station 20 as soon as it detects that thelocation area has changed based on the received LAI in systeminformation in SI6 will trigger the LAU by sending the Location AreaUpdate Request message to the new cell 28. Unlike this fourthembodiment, in conventional GERAN in dedicated mode this procedure canonly be performed after the release of the connection thus not during anongoing call.

In a variation of the fourth embodiment there is only a partialregistration update while the UE/mobile station 20 is in the dedicatedmode. It is partial because the network does not provide the full EPLMNlist_(new cell), to the UE/mobile station 20. As noted above it isconventional practice, restricted to VOCS/VES, that the network provideto a mobile station in dedicated mode the SYSTEM INFORMATION TYPE 6message which contains the location area identity and therefore the PLMNID. This SI6 message is expanded as detailed in the teachings above tosupport the PLMN validity detection when both the old cell 24 and theUE/mobile station 20 support interworking with CSG cells 30 in thededicated mode. In this variation the network/old cell 24 does notnecessarily make a PLMN validity detection itself before sending the SI6message. Instead, based on the PLMN ID the UE/mobile station 20 receivesin SI6 (or another message) the UE/mobile station 20 could itself detectthat {rPLMN, EPLMN list}_(old cell) ∩{PLMN}_(new cell)=∩.

This PLMN validity detection by the UE/mobile station 20 mayalternatively be triggered by a PLMN validity detection done by thenetwork itself, and signaled to the UE/mobile station 20 by the old cell24 at handover such as the above-mentioned RR HANDOVER COMMAND message.In one implementation of this variation to the fourth embodiment, theUE/mobile station 20 in the dedicated mode can perform the PLMN validitycheck by using the {PLMN}_(new cell) instead of the {rPLMN, EPLMNList}_(old cell) to perform the access check in order to determinewhether CSG cells 30 are allowed or not. Or in another implementation ofthis variation to the fourth embodiment the UE/mobile station 20 in thededicated mode can perform the PLMN validity check by using the{PLMN}_(new cell) in addition to the {rPLMN, EPLMN list}_(old cell) toperform the access check in order to determine whether CSG cells 30 areallowed or not.

As noted for all of the above embodiments and implementations, they eachresolve either the false match or the missed match errors to someextent, but none alone are a complete solution to both those errortypes. Suggested combinations of the above embodiments to form acomplete solution for addressing both error types include at least thefollowing combinations:

-   -   the first embodiment with the third embodiment; the second        embodiment with the third embodiment;    -   the first embodiment with the fourth embodiment;    -   the second embodiment with the fourth embodiment;    -   the first embodiment with the first implementation of the        variation of the fourth embodiment; and    -   the first embodiment with the second implementation of the        variation of the fourth embodiment.

As noted briefly above these solutions are not limited to only handingover from a GERAN cell but are readily extended to other RATs, forexample handing over in UTRAN and E-UTRAN where the PLMN/EPLMN list isexpected to change but where no location area, routing area or trackingarea is to be performed after handover.

FIG. 2 is a signaling flow diagram illustrating how the new informationelement (IE) PLMN/EPLMNList CHANGE Indication is added by the old cell24 to the handover signaling according to various embodiments of theseteachings. This information element indicates to the UE/mobile station20 whether an EPLMN list will change due to the location area change.The signaling in FIG. 2 includes the serving cell 24, the serving cell'sMSC 22, the target cell 28 and the target cell's MSC 26. The private/CSGcell is not shown specifically in FIG. 2 but it is in background fromwhich the UE 20 can receive its broadcast PLMN-IDa and CSG-IDa.

The signaling flow is depicted in FIG. 2, which like FIG. 1 has the UEhanding over from BSS-A (serving or old cell 24) under control of MSC-A11 to BSS-B (target or new cell 28) under control of MSC-B 26. The BSS-A24 will include in its handover required message 202 to its MSC-A 24 theEPLMN1 list which is valid for MSC-A 24. The MSC-A 24 will then signalto the MSC-B 26 a handover prepare message 204 which also includes theEPLMN1 list. MSC-B 26 checks with the visiting location register VLR-Bfor the handover as is conventional, and compares the PLMN1/EPLMN1 listwhich is valid for MSC-A 24 against its own PLMN2/EPLMN2 list which isvalid for MSC-B 26. MSC-B 26 then includes an indicator in its handoverrequest message 206 to its BSS-B 28, that indicator telling whether ornot the PLMN1/EPLMN1 was identical to the PLMN2/EPLMN2. In various ofthe above embodiments the BSS-B 28 or ESS-A 24 then signals to the UE 20the indicator, or the PLMN2, or both. Prior to the handover the BSS-A 24would signal the indicator in the handover command 208. The MSC-B 26shall be able to set the PLMN/EPLMNList_CHANGE Indicator on theAinterface (which is the interface between the MSC and the BSS) at steps3 and 4 in FIG. 2 based on the indicator received from the old MSC-A 24.

One exemplary implementation of the inter-MSC procedure is depicted insteps 1 and 2 in FIG. 2; the MSC-A 24 may also set the E-PLMN ListIndicator based on the target cell ID in the Handover Required message202 if it can determine that another PLMN and E-PLMN list different fromits current list is valid in the new cell. So that both the UE 20 andthe various network nodes 22, 24, 26, 28 all understand the messagingchanges according to these teachings, in 3GPP TS 48.008 may be amendedto add the PLMN/EPLMNList_CHANGE indicator to the Handover Request 206on the A interface, and 3GPP TSG 44.018 may be amended to add that sameindicator to the RR Handover Command 208.

The purpose of the PLMN/EPLMNList_CHANGE Indication information elementis to indicate whether the PLMN/EPLMNList_CHANGE in the new cell 28after handover will change or not, while the UE is in the dedicatedmode. FIGS. 3A-B illustrates one exemplary coding for thePLMN/EPLMNList_CHANGE Indication information element, which is a type 1information element. As can be seen at FIG. 3A, the actual changeindicator 302 is a single bit, further explained at FIG. 3B,

FIGS. 4A-B are logic flow diagrams which each describes the aboveexemplary embodiments of the invention. Each represents results fromexecuting a computer program or an implementing algorithm stored in thelocal memory of the UE 20 (as to FIG. 4B) or one or more of the networkelements 22, 24, 26, 28 (as to FIG. 4A), as well as illustrating theoperation of a method and a specific manner in which the processor andmemory with computer program/algorithm are configured to cause that UE20 and the various network elements (or one or more components thereof)to operate. The various blocks shown in each of FIGS. 4A-B may also beconsidered as a plurality of coupled logic circuit elements constructedto carry out the associated function(s), or specific result or functionof strings of computer program code stored in a computer readablememory. The serving and target cells recited at FIGS. 4A-B are in therespective positions of the old and new cells in the examples above.

Such blocks and the functions they represent are non-limiting examples,and may be practiced in various components such as integrated circuitchips and modules, and that the exemplary embodiments of this inventionmay be realized in an apparatus that is embodied as an integratedcircuit. The integrated circuit, or circuits, may comprise circuitry (aswell as possibly firmware) for embodying at least one or more of a dataprocessor or data processors, a digital signal processor or processors,baseband circuitry and radio frequency circuitry that are configurableso as to operate in accordance with the exemplary embodiments of thisinvention.

First consider FIG. 4A from the network-side perspective. At block 402it is detected that for a UE there is a change to at least one of a PLMNand a list of equivalent PLMNs between a serving cell and a target cell.Thereafter at block 404 one of these cells sends to the UE an indicationof the detected change during a handover of the UE (which is in adedicated or connected mode) from the serving cell to the target cell.The further blocks of FIG. 4A represent some of the above specificimplementations and may be combined variously with one another to modifyor add to blocks 402 and 404.

Block 406 has the detecting from the equations given above. Thedetecting may be checking any of:

-   -   the PLMN of the serving cell and the list of equivalent PLMNs of        the serving cell are identical to the PLMN of the target cell        and the list of equivalent PLMNs of the target cell;    -   the PLMN of the target cell is identical to any of the PLMN of        the serving cell and any PLMN in the list of equivalent PLMNs of        the serving cell; and    -   the PLMN of the serving cell is identical to any of the PLMN of        the target cell and any PLMN in the list of equivalent PLMNs of        the target cell.

According to the first and second embodiments above, the detecting atblock 402 is by the target cell and block 408 provides that theindication is one bit in a PLMN/EPLMNList_cHANGE indication informationelement which the serving cell sends in a HANDOVER COMMAND message. Inthis case it is the target cell that detected the change. The targetcell informs the serving cell of that a change was detected, such asthrough a Layer 3 Information message, and it is the serving cell whichinforms the information element to the UE.

Adding the third embodiment to block 408, at block 410 the target celltriggers in the UE a location or registration area update procedureduring which the target cell sends to the UE the PLMN of the targetcell.

Adding the fourth embodiment to block 408, at block 412 the PLMN of thetarget cell is sent to the UE in either a SI6 message (sent by thetarget cell) or a HANDOVER COMMAND message (sent by the serving cell).In one implementation of the fourth embodiment the PLMN of the targetcell is contained within a location area identifier of the target cellwhich is included within the SI6 or handover command message; in anotherimplementation the PLMN of the target cell is sent by target cell in alocation or registration update procedure that is triggered in the UE bythe target cell.

Or for the case of the fourth embodiment alone the indication of block404 may be the PLMN of the target cell which the serving cell sends inone of a SI6 message or a HANDOVER COMMAND message.

Now consider FIG. 4B from the UE-side perspective. At block 452, duringa handover of a HE in a dedicated or connected mode from a serving cellto a target cell, the UE receives signaling indicating that there is achange to at least one of a public land mobile network PLMN and a listof equivalent PLMNs between a serving cell and a target cell. And atblock 454 the UE utilizes at least one updated PLMN to check whether aprivate cell is allowed for the UE. The further blocks of FIG. 4Brepresent some of the above specific implementations and may be combinedvariously with one another to modify or add to blocks 452 and 454.

Block 456 modifies block 452 in that the indication is one bit in aPLMN/EPLMNList_CHANGE indication information element which the UEreceives from the serving cell in a HANDOVER COMMAND message.

Block 458 has the first embodiment in which the at least one updated.PLMN is obtained during a location or registration area update; and theUE refrains from reporting private cells/CSGs after the handover untilthe location or registration area update.

Whether or not the UE refrains from reporting, the combined first andthird embodiments are represented by block 460 in which the at least oneupdated PLMN is the PLMN of the target cell that the UE obtains during alocation or registration area update that is triggered in the UE by thetarget cell.

The combined first and fourth embodiments are represented by block 462,in which the at least one updated PLMN comprises the PLMN of the targetcell which the apparatus receives from the target cell in one of asystem information SI6 message or a location or registration updatemessage. In the fourth embodiment it is the UE that requests of thetarget cell a location area update in response to receiving the PLMN ofthe target cell. That PLMN of the target cell may be contained within alocation area identifier of the target cell which is included within theSI6 message.

In the first implementation of the fourth embodiment the UE utilizes atblock 452 the received PLMN of the target cell in place of or instead ofthe PLMN of the serving cell and in place of/instead of the EPLMN listof the serving cell to check whether the private/CSG cell is allowed forthe UE. In the second implementation of the fourth embodiment the UEutilizes at block 452 the received PLMN of the target cell in additionto the PLMN of the serving cell and in addition to the EPLMN list of theserving cell to check whether the private/CSG cell is allowed for theUE.

Reference is now made to FIG. 5 for illustrating a simplified Nockdiagram of various electronic devices and apparatus that are suitablefor use in practicing the exemplary embodiments of this invention. InFIG. 5 there is MSC-A 22 controlling cell-A 24 and MSC-B 26 controllingcell-B 28 as in FIG. 1, with a UE/mobile station 20 having wirelesslinks with each and handing over from cell-A 24 to cell-B 28 whilechecking to see if CSG cell-C 30 is an allowed cell for the UE/mobilestation 20.

The UE/mobile station 20 includes processing means such as at least onedata processor (DP) 20A, storing means such as at least onecomputer-readable memory (MEM) 20B storing at least one computer program(PROG) 20C, and also communicating means such as a transmitter TX 20Dand a receiver RX 20E for bidirectional wireless communications via oneor more antennas 20F. Also shown for the UE 20 at block 20G is the PLMNcheck which it does in certain embodiments as detailed above.

The MSC-A 22 and also the cell-A 24 similarly includes processing meanssuch as at least one data processor (DP) 22A/24A, storing means such asat least one computer-readable memory (MEM) 22B/24B storing at least onecomputer program (PROG) 22C/24C, and the cell-A has communicating meanssuch as a transmitter TX 24D and a receiver RX 24E for bidirectionalwireless communications with the UE 20 via one or more antennas 22F. TheMSC-A 22 has communication means such as a modem 22H for communicationsover the control link with the cell-A 24. The MSC-A 22 and the cell-A 24may also have a PLMN checking module or program 22G/24G similar to thatof the HE the Similarly, The MSC-B 26 and also the cell-B 28 alsoincludes processing means such as at least one data processor (DP)26A/28A, storing means such as at least one computer-readable memory(MEM) 26B/28B storing at least one computer program (PROG) 26C/28C, andthe cell-B has communicating means such as a transmitter TX 28D and areceiver RX 28E for bidirectional wireless communications with the UE 20via one or more antennas 281F. The MSC-B 26 has communication means suchas a modem 26H for communications over the control link with the cell-B28. The MSC-B 26 and the cell-B 28 may also have a PLMN checking moduleor program 26G/280 similar to that of the UE 20.

While a modem is shown for the MSCs 22, 26, the UE 20 as well as thecell-A 24 and the cell-B 28 are also assumed to include a modem, such asfor example in a RF front end chip which also carries their respectivetransmitters and receivers.

At least one of the PROGs 20C in the UE 20 is assumed to include programinstructions that, when executed by the associated DP 20A, enable thedevice to operate in accordance with the exemplary embodiments of thisinvention, as detailed above. The various MSCs 22, 26 as well as thecells 24, 28 also have software stored in their respective MEMs toimplement certain aspects of these teachings. In these regards theexemplary embodiments of this invention may be implemented at least inpart by computer software stored on the MEM 20B, 2213, 24B, 26B, 28Bwhich is executable by the DP 20A of the UE 20 and/or by the DP22A/24A/26A/28A of the respective network nodes 22, 24, 26, 28, or byhardware, or by a combination of tangibly stored software and hardware(and tangibly stored firmware). Electronic devices implementing theseaspects of the invention need not be the entire devices as depicted atFIG. 5, but exemplary embodiments may be implemented by one or morecomponents of same such as the above described tangibly stored software,hardware, firmware and DP, or a system on a chip SOC or an applicationspecific integrated circuit ASIC.

Various embodiments of the computer readable MEMs 20B, 22B, 2413, 2613and 2813 include any data storage technology type which is suitable tothe local technical environment, including but not limited tosemiconductor based memory devices, magnetic memory devices and systems,optical memory devices and systems, fixed memory, removable memory, discmemory, flash memory, DRAM, SRAM, EEPROM and the like. Variousembodiments of the DPs 20A, 22A, 24A, 26A and 28A include but are notlimited to general purpose computers, special purpose computers,microprocessors, digital signal processors (DSPs) and multi-coreprocessors.

Further, some of the various features of the above non-limitingembodiments may be used to advantage without the corresponding use ofother described features. The foregoing description should therefore beconsidered as merely illustrative of the principles, teachings andexemplary embodiments of this invention, and not in limitation thereof.

1. An apparatus comprising a user equipment for use in maintainingclosed subscriber group cells, the apparatus comprising a processingsystem arranged to cause the apparatus to: during a handover of the userequipment in a dedicated or connected mode from a serving cell to atarget cell, receive signaling indicating that there is a change to atleast one of a public land mobile network PLMN and a list of equivalentPLMNs between a serving cell and a target cell, and utilize at least oneupdated PLMN to check whether a private cell is allowed for the userequipment; the at least one updated PLMN comprises the PLMN of thetarget cell which the apparatus receives from the target cell in asystem information SI6 message; the processing system is arranged tocause the apparatus to at least further request of the target cell alocation area update in response to receiving the PLMN of the targetcell; the PLMN of the target cell is contained within a location areaidentifier of the target cell which is included within the SI6 message;the processing system is arranged to cause the apparatus to utilize thereceived PLMN of the target cell in place of the PLMN of the servingcell and in place of a list of equivalent PLMNs of the serving cell tocheck whether the private cell is allowed for the user equipment.
 2. Theapparatus according to claim 1, wherein the indication is one bit in aPLMN/EPLMNList_CHANGE indication information element which is receivedfrom the serving cell in a HANDOVER COMMAND message.
 3. The apparatusaccording to claim 1, wherein the at least one updated PLMN is obtainedduring a location or registration area update; and the processing systemis arranged to cause the apparatus to refrain from reporting privatecells after the handover until the location or registration area update.4. The apparatus according to claim 1, wherein the at least one updatedPLMN is the PLMN of the target cell which the user equipment obtainsduring a location or registration area update that is triggered in theuser equipment by the target cell.
 5. The apparatus according to claim1, wherein the processing system is arranged to cause the apparatus toutilize the received PLMN of the target cell in addition to the PLMN ofthe serving cell and in addition to a list of equivalent PLMNs of theserving cell to check whether the private cell is allowed for the userequipment.